1. Field of the Invention
The present invention relates generally to a process for forming polymers comprising directly bonded arylene groups, and, more particularly, to a photochemical vapor deposition process for depositing thin layers of such polymers on a substrate.
2. Description of the Background Art
A variety of dielectric or insulating materials are used in the fabrication of semiconductor devices and circuits to provide a layer of electrical insulation between adjacent conductive areas. In addition, such materials are used to provide a surface passivation layer to protect substrate surfaces or to provide a mask for selective processes such as etching or ion implantation. Typical materials used include silicon dioxide, silicon nitride, polyimides and polymers of the polyphenylene class of compounds.
A known method for forming polyparaphenylene is by the reaction in solution between p-dibromobenzene and magnesium and NiCl.sub.2 (bipyridine), as described, for example, by T. Yamamoto, Y. Hayashi, and A. Yamamoto in Bul. Chem. Soc. Jap., Vol. 51, 1978, at page 2091. Another known method for forming polyparaphenylene is by the oxidative cationic polymerization of benzene as described by P. Kovacic and A. Kyriakis in J. Am. Chem. Soc., Vol. 85, 1963, at page 454 and by P. Kovacic and J. Oziomek, in J. Org. Chem., Vol. 29, 1964, at page 100. The product of these methods is a brown infusible powder which must be sintered at a temperature above 300.degree. C. and under increased pressure to form it into the desired shape. However, the sintering process tends to degrade the polymer and the resulting product has less than the theoretical maximum density, resulting in loss of contact between particles and decrease in electrical conductivity. The latter property is important for forming conductive polymers, as discussed immediately below. Moreover, since the polymers must be pressed into the desired shape it is not possible to form very thin films which conform to the substrate.
In addition, it has recently been proposed to dope polyparaphenylene to produce a conducting polymer, as described, for example, by D. M. Ivory et al, in J. Chem. Phys., Vol. 71, 1979, at page 1506. These conducting polymers can be used in lightweight batteries, such as for an all-electric automobile, in solar cells, as wire and cable sheathing, and as electromagnetic shielding. However, progress in this area has been limited by the above noted fabrication difficulties associated with polyparaphenylene.
Thus, the need exists for a low-temperature process for forming polyparaphenylene. Further, there exists a need for a process for forming thin films of polyparaphenylene having desirable physical and electrical properties for the applications discussed above.